Fuel cell module

ABSTRACT

A fuel cell module includes a fuel cell stack, a partial oxidation reformer for reforming a mixed gas of a raw fuel and an oxygen-containing gas, an exhaust gas combustor for combusting a fuel exhaust gas and an oxygen-containing exhaust gas discharged from the fuel cell stack thereby to produce a combustion gas, and a heat exchanger for raising the temperature of the oxygen-containing gas by heat exchange with the combustion gas. The heat exchanger is provided on one side of the fuel cell stack, and the partial oxidation reformer and the exhaust gas combustor are provided on the other side of the fuel cell stack. The partial oxidation reformer is provided so as to surround the exhaust gas combustor.

TECHNICAL FIELD

The present invention relates to a fuel cell module including a fuelcell stack formed by stacking a plurality of fuel cells for generatingelectricity by electrochemical reactions of a fuel gas and anoxygen-containing gas.

BACKGROUND ART

Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte ofion-conductive solid oxide such as stabilized zirconia. The electrolyteis interposed between an anode and a cathode to form an electrolyteelectrode assembly (hereinafter also referred to as MEA). Theelectrolyte electrode assembly is interposed between separators (bipolarplates). In use, generally, predetermined numbers of the electrolyteelectrode assemblies and the separators are stacked together to form afuel cell stack.

Normally, a hydrogen gas produced from hydrocarbon based raw fuel by areformer is used as a fuel gas supplied to the fuel cell. In thereformer, in general, a reformed gas (fuel gas) is produced, e.g., byapplying partial oxidation reforming or steam reforming to suchhydrocarbon based raw fuel, e.g., fossil fuel such as metal or LNG.

In this case, since the partial oxidation reformer induces exothermicreaction, the reaction can be started at relatively low temperature andoperation can be started efficiently, and the follow up performance isgood. In contrast, the steam reformer has good reforming efficiency.

For example, a fuel cell disclosed in Japanese Laid-Open PatentPublication No. 2010-218888 (hereinafter referred to as ConventionalTechnique 1) is known. In the fuel cell system, as shown in FIG. 4, afuel processing system 1 a is provided. The fuel processing system 1 ahas a reformer 2 a and a burner combustor 3 a.

In the fuel cell system, an air supply apparatus 5 a is controlled basedon an indicator value of a flow rate meter 4 a. When the air is notsupplied by the air supply apparatus 5 a, the indicator value of theflow rate meter 4 a is corrected to a value indicating that the flowrate is zero. As a result, in the structure, since the indicator valueof the flow rate meter 4 a indicates the flow rate of the actualsupplied air, the flow rate of the air supplied by the air supplyapparatus 5 a can be regulated with a high degree of accuracy.

Further, in a partial oxidation reformer disclosed in Japanese Laid-OpenPatent Re-publication WO 01/047800 (PCT) (hereinafter referred to asConventional Technique 2), as shown in FIG. 5, a reformer 1 b has a dualwall structure including a housing 2 b, and partition walls 3 b, 3 bprovided in the housing 2 b. A reforming reaction unit 4 b is providedbetween the partition walls 3 b, and a space between the housing 2 b andthe partition wall 3 b is used as a raw material gas passage 5 b aroundthe reforming reaction unit 4 b.

Heat insulation of the reforming reaction unit 4 b is performed by theraw material gas passage 5 b to reduce non-uniformity in the temperatureinside the reforming reaction unit 4 b. The raw material gas in the rawmaterial gas passage 5 b is heated beforehand by the reaction heat inthe reforming reaction unit 4 b. Thus, the heat efficiency in thereformer 1 b is improved by self-heat collection, and a preheater forheating the raw material gas beforehand is formed integrally between theraw material gas passage 5 b and the reforming reaction unit 4 b.

According to the disclosure, in the structure, in the reforming reactionunit 4 b, in the case where a hydrogen rich reforming gas is produced byreaction including partial oxidation from the raw material gas,non-uniformity in the temperature inside the reforming reaction unit 4 bis reduced, improvement in the heat efficiency is achieved, and thereformer has a simple and compact structure.

SUMMARY OF INVENTION

However, in Conventional Technique 1, the flow rate of the fluid iscorrected, and correction based on the temperature is not considered.Thus, if the volume varies depending on the temperature range, thesupplied fluid may exceed the fluid control range undesirably. Further,in Conventional Technique 1, since a solid polymer electrolyte fuel cellstack is used, it is required to cool reformed gas discharged from thereformer 2 a. Therefore, a large loss in heat energy occurs, whichresults in a problem that the heat energy cannot be utilizedefficiently.

Further, in Conventional Technique 2, since heat exchange occurs betweenthe raw material gas and the reformed gas, the temperature of thereformed gas is decreased. Further, since the reformer for solid polymerelectrolyte fuel cells is adopted, it is required to decrease thetemperature of the reformed gas when the reformed gas is transferred toa CO removal device, and the heat energy cannot be utilized efficiently.

The present invention has been made to solve the problems of this type,and an object of the present invention is to provide a fuel cell modulewhich makes it possible to suppress loss of heat energy, facilitatethermally self-sustaining operation, and achieve reduction in the costand size.

The present invention relates to a fuel cell module including a fuelcell stack formed by stacking a plurality of fuel cells in a stackingdirection for generating electricity by electrochemical reactions of afuel gas and an oxygen-containing gas, a partial oxidation reformer forreforming a mixed gas of a raw fuel chiefly containing hydrocarbon andan oxygen-containing gas thereby to produce the fuel gas, and supplyingthe fuel gas to the fuel cell stack, an exhaust gas combustor forcombusting the fuel gas discharged from the fuel cell stack as a fuelexhaust gas and the oxygen-containing gas discharged from the fuel cellstack as an oxygen-containing exhaust gas thereby to produce acombustion gas, and a heat exchanger for raising the temperature of theoxygen-containing gas by heat exchange with the combustion gas, andsupplying the oxygen-containing gas to the fuel cell stack.

The heat exchanger is provided on one side of the fuel cell stack, andthe partial oxidation reformer and the exhaust gas combustor areprovided on the other side of the fuel cell stack. The partial oxidationreformer is provided so as to surround the exhaust gas combustor.

In the present invention, the heat exchanger is provided on one side ofthe fuel cell stack, and the partial oxidation reformer and the exhaustgas combustor are provided on the other side of the fuel cell stack.Thus, heat release from the fuel cell stack is minimized, and variationin the temperature distribution in the fuel cell stack is reduced.Accordingly, the heat energy loss can be suppressed, and thermallyself-sustaining operation is facilitated easily.

Further, the partial oxidation reformer is provided so as to surroundthe exhaust gas combustor. In the structure, in the state where theself-ignition temperature is maintained, the fuel exhaust gas and theoxygen-containing exhaust gas discharged from the fuel cell stack can besupplied into the exhaust gas combustor. Accordingly, in the exhaust gascombustor, stability in combustion is improved suitably, and thermallyself-sustaining operation is facilitated easily.

Moreover, as a reformer, only the partial oxidation reformer is providedwithout requiring any steam reformer. Thus, since the water supplysystem for supplying water vapor can be omitted, reduction in the numberof parts can be achieved, and reduction in the cost and size of theentire fuel cell module is achieved.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing a structure of a fuel cellsystem incorporating a fuel cell module according to an embodiment ofthe present invention;

FIG. 2 is a flow chart illustrating an operational sequence of the fuelcell system;

FIG. 3 is a diagram showing an optimal map of a partial oxidationreformer of the fuel cell module;

FIG. 4 is a view schematically showing a fuel cell system disclosed inConventional Technique 1; and

FIG. 5 is a view schematically showing a partial oxidation reformerdisclosed in Conventional Technique 2.

DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1, a fuel cell system 10 incorporates a fuel cellmodule 12 according to an embodiment of the present invention, and thefuel cell system 10 is used in various applications, includingstationary and mobile applications. For example, the fuel cell system 10is mounted on a vehicle.

The fuel cell system 10 includes a fuel cell module (SOFC module) 12 forgenerating electrical energy in power generation by electrochemicalreactions of a fuel gas (a gas produced by mixing a hydrogen gas,methane, and carbon monoxide) and an oxygen-containing gas (air), a rawfuel supply apparatus (including a fuel gas pump) 14 for supplying a rawfuel (e.g., city gas) to the fuel cell module 12, an oxygen-containinggas supply apparatus (including an air pump) 16 for supplying theoxygen-containing gas to the fuel cell module 12, and a control device18 for controlling the amount of electrical energy generated in the fuelcell module 12.

The fuel cell module 12 includes a fuel cell stack 22 formed by stackinga plurality of solid oxide fuel cells 20 in a vertical direction(indicated by arrow A). For example, the fuel cell 20 includes anelectrolyte electrode assembly 30 (MEA). The electrolyte electrodeassembly 30 includes a cathode 26, an anode 28, and an electrolyte 24interposed between the cathode 26 and the anode 28. For example, theelectrolyte 24 is made of ion-conductive solid oxide such as stabilizedzirconia.

A cathode side separator 32 and an anode side separator 34 are providedon both sides of the electrolyte electrode assembly 30. Anoxygen-containing gas flow field 36 for supplying an oxygen-containinggas to the cathode 26 is formed in the cathode side separator 32, and afuel gas flow field 38 for supplying a fuel gas to the anode 28 isformed in the anode side separator 34. As the fuel cell 20, varioustypes of conventional SOFC can be adopted.

An oxygen-containing gas supply passage 40 a, an oxygen-containing gasdischarge passage 40 b, a fuel gas supply passage (fuel gas inlet) 42 a,and a fuel gas discharge passage 42 b extend through the fuel cell stack22. The oxygen-containing gas supply passage 40 a is connected to aninlet of each oxygen-containing gas flow field 36, the oxygen-containinggas discharge passage 40 b is connected to an outlet of eachoxygen-containing gas flow field 36, the fuel gas supply passage 42 a isconnected to an inlet of each fuel gas flow field 38, and the fuel gasdischarge passage 42 b is connected to an outlet of each fuel gas flowfield 38.

The fuel cell module 12 includes a partial oxidation reformer (POX) 44for reforming a mixed gas of a raw fuel chiefly containing hydrocarbonand the oxygen-containing gas, an exhaust gas combustor 46 forcombusting the fuel gas discharged from the fuel cell stack 22 as a fuelexhaust gas, and the oxygen-containing gas discharged from the fuel cellstack 22 as an oxygen-containing exhaust gas thereby to produce acombustion gas, and a heat exchanger 48 for raising the temperature ofthe oxygen-containing gas by heat exchange with the combustion gas, andsupplying the oxygen-containing gas to the fuel cell stack 22.

Basically, the fuel cell module 12 is made up of the fuel cell stack 22and FC (fuel cell) peripheral equipment 50. The FC peripheral equipment50 includes the partial oxidation reformer 44, the exhaust gas combustor46, and the heat exchanger 48. The partial oxidation reformer 44 isprovided around the exhaust gas combustor 46. The exhaust gas combustor46 has a columnar (or square pillar) outer shape. The partial oxidationreformer 44 has a ring shape (or square pillar shape) containing thereinthe exhaust gas combustor 46.

The heat exchanger 48 is provided on one side of the fuel cell stack 22,more preferably, on one side of the fuel cells 20 in the stackingdirection indicated by the arrow A, and the partial oxidation reformer44 and the exhaust gas combustor 46 are provided on the other side ofthe fuel cell stack 22, more preferably, on the other side of the fuelcells 20 in the stacking direction indicated by the arrow A.

The direction in which the fuel cells 20 are stacked is the same as thedirection of gravity. Stated otherwise, the heat exchanger 48 isprovided above the fuel cell stack 22 in the direction of gravity, andthe partial oxidation reformer 44 and the exhaust gas combustor 46 areprovided below the fuel cell stack 22 in the direction of gravity.

The partial oxidation reformer 44 is filled with partial oxidationcatalyst (not shown). An ignition device (not shown) such as an igniteror a glow for ignition at the time of starting operation is provided onthe partial oxidation reformer 44. The partial oxidation reformer 44 hasa mixed gas inlet port 52 a and a fuel gas outlet port 52 b. A raw fuelafter desulfurization is supplied into the partial oxidation reformer 44through the mixed gas inlet port 52 a, and the reformed gas (fuel gas)after partial oxidation reforming of the raw fuel is discharged from thepartial oxidation reformer 44 through the fuel gas outlet port 52 b.

A combustion chamber 54 is provided in the exhaust gas combustor 46. Anoxygen-containing exhaust gas inlet port 56, a fuel exhaust gas inletport 58, and an exhaust gas outlet port 60 are connected to thecombustion chamber 54. At the combustion chamber 54, an ignition device(not shown) such as an igniter or a glow for ignition of the mixed gasof the reduction gas (fuel gas) and the oxygen-containing gas at thetime of starting operation is provided.

A heating space containing a plurality of oxygen-containing gas pipes(not shown) is formed in the heat exchanger 48, and theoxygen-containing gas flowing through the oxygen-containing gas pipes isheated by the hot exhaust gas (combustion gas) supplied to the heatingspace. The heat exchanger 48 has an oxygen-containing gas supply port 62a and an oxygen-containing gas discharge port 62 b connectedrespectively to the inlets and the outlets of the oxygen-containing gaspipes, and an exhaust gas supply port 64 a and an exhaust gas dischargeport 64 b connected to the heating space.

The fuel gas supply passage 42 a of the fuel cell stack 22 and the fuelgas outlet port 52 b of the partial oxidation reformer 44 are connectedto each other through a fuel gas channel 66. The oxygen-containing gasdischarge passage 40 b of the fuel cell stack 22 and theoxygen-containing exhaust gas inlet port 56 of the exhaust gas combustor46 are connected to each other through an oxygen-containing exhaust gaschannel 68. The fuel gas discharge passage 42 b of the fuel cell stack22 and the fuel exhaust gas inlet port 58 of the exhaust gas combustor46 are connected to each other through a fuel exhaust gas channel 70.The oxygen-containing gas supply passage 40 a of the fuel cell stack 22and the oxygen-containing gas discharge port 62 b of the heat exchanger48 are connected to each other through an oxygen-containing gas channel72.

One end of a combustion gas pipe 74 a is connected to the exhaust gasoutlet port 60 of the exhaust gas combustor 46, and the other end of thecombustion gas pipe 74 a is connected to the fuel cell stack 22. One endof a combustion gas pipe 74 b for discharging the exhaust gas(combustion gas) is connected to the fuel cell stack 22, and the otherend of the combustion gas pipe 74 b is connected to the exhaust gassupply port 64 a of the heat exchanger 48. One end of a combustion gaspipe 74 c is connected to the exhaust gas discharge port 64 b of theheat exchanger 48, and the other end of the combustion gas pipe 74 c isconnected to external heat equipment 76. For example, the external heatequipment 76 includes a water heater or a thermoelectric converter.

The raw fuel supply apparatus 14 has a raw fuel channel 80 a, and theraw fuel channel 80 a is connected to an inlet of a desulfurizer 82 forremoving sulfur compounds in the city gas (raw fuel). One end of a rawfuel supply channel 80 b is connected to the outlet of the desulfurizer82, and the other end of the raw fuel supply channel 80 b is connectedto the mixed gas inlet port 52 a of the partial oxidation reformer 44.

The oxygen-containing gas supply apparatus 16 has an oxygen-containinggas supply channel 84, and the oxygen-containing gas supply channel 84is connected to an oxygen-containing gas regulator valve 86. Theoxygen-containing gas regulator valve 86 distributes theoxygen-containing gas to a first oxygen-containing gas supply channel 88a and a second oxygen-containing gas supply channel 88 b. The firstoxygen-containing gas supply channel 88 a is connected to theoxygen-containing gas supply port 62 a of the heat exchanger 48, and thesecond oxygen-containing gas supply channel 88 b is connected to the rawfuel supply channel 80 b, at a position between the desulfurizer 82 andthe partial oxidation reformer 44.

The partial oxidation reformer 44 is a preliminary reformer forpartially oxidation-reforming higher hydrocarbon (C₂₊) such as ethane(C₂H₆), propane (C₃H₈), and butane (C₄H₁₀) in the city gas (raw fuel)thereby to produce the fuel gas chiefly containing hydrogen, and CO. Theoperating temperature of the partial oxidation reformer 44 is severalhundred ° C.

The fuel cell 20 operates at high temperature, such as several hundred °C. Hydrogen and CO contained in the fuel gas are supplied to a portionof the electrolyte 24 that is positioned adjacent to the anode 28.

Next, operation of the fuel cell system 10 will be described below withreference to a flow chart shown in FIG. 2.

Firstly, at the time of starting operation of the fuel cell system 10,the opening degree of the oxygen-containing gas regulator valve 86 isdetermined. More specifically, the raw fuel supply apparatus 14 isoperated, and the opening degree of the oxygen-containing gas regulatorvalve 86 is adjusted such that the air (oxygen-containing gas) and theraw fuel such as city gas (containing CH₄, C₂H₆, C₃H₈, C₄H₁₀) requiredfor partial oxidation reforming are supplied (step S1). The control ofthe partial oxidation reforming is performed based on the air fuel ratio(O₂/C) (the number of moles of oxygen in the supplied air/the number ofmoles 25, of carbon in the supplied raw fuel). The air and raw fuel aresupplied to the partial oxidation reformer 44 at the optimum air-fuelratio.

In the raw fuel supply apparatus 14, the raw fuel supplied to the rawfuel channel 80 a is desulfurized by the desulfurizer 82, and then theraw fuel is supplied to the mixed gas inlet port 52 a of the partialoxidation reformer 44 through the raw fuel supply channel 80 b. In theoxygen-containing gas supply apparatus 16, after the air is supplied tothe oxygen-containing gas supply channel 84, the air is distributed tothe first oxygen-containing gas supply channel 88 a and to the secondoxygen-containing gas supply channel 88 b at their respectivepredetermined amounts through the oxygen-containing gas regulator valve86. The air distributed to the second oxygen-containing gas supplychannel 88 b is mixed with the raw fuel in the raw fuel supply channel80 b, and the mixture containing the air is supplied to the mixed gasinlet port 52 a of the partial oxidation reformer 44.

In the partial oxidation reformer 44, ignition is caused by anunillustrated ignition device, and then partial oxidation reforming bythe partial oxidation reformer 44 is started. For example, if O₂/C=0.5,partial oxidation reaction (2CH₄+O₂→4H₂+2CO) occurs. The partialoxidation reaction is an exothermic reaction, and a hot reduction gas(fuel gas) (at about 600° C.) is produced by the partial oxidationreformer 44.

The hot reduction gas is supplied to the fuel gas supply passage 42 a ofthe fuel cell stack 22 through the fuel gas channel 66. In the fuel cellstack 22, after the hot reduction gas flows through the fuel gas flowfield 38, the fuel gas is discharged from the fuel gas discharge passage42 b to the fuel exhaust gas channel 70. The reduction gas is introducedfrom the fuel exhaust gas inlet port 58 communicating with the fuelexhaust gas channel 70, into the combustion chamber 54 of the exhaustgas combustor 46.

On the other hand, in the oxygen-containing gas supply apparatus 16, theair is supplied to the first oxygen-containing gas supply channel 88 a,and then is introduced from the oxygen-containing gas supply port 62 ainto the heat exchanger 48. The air is heated by the combustion gas (tobe described later) supplied into the heating space (heat exchangebetween the air and the combustion gas occurs) while the air is movingthrough the oxygen-containing gas pipes. The heated air is suppliedthrough the oxygen-containing gas channel 72 to the oxygen-containinggas supply passage 40 a of the fuel cell stack 22.

In the fuel cell stack 22, after the heated air flows through theoxygen-containing gas flow field 36, the air is discharged from theoxygen-containing gas discharge passage 40 b into the oxygen-containingexhaust gas channel 68. Since the oxygen-containing exhaust gas channel68 is opened to the combustion chamber 54 of the exhaust gas combustor46, the air is supplied into the combustion chamber 54. Therefore, thefuel exhaust gas and the oxygen-containing exhaust gas flow into thecombustion chamber 54. When the temperature in the combustion chamber 54exceeds the self-ignition temperature of the fuel gas, combustion by theair and the fuel gas is started in the combustion chamber 54. If thetemperature in the combustion chamber 54 does not exceed theself-ignition temperature, ignition is caused by an ignition device (notshown) (step S2).

The combustion gas produced in the combustion chamber 54 flows from theexhaust gas outlet port 60, and the combustion gas is supplied to thefuel cell stack 22 through the combustion gas pipe 74 a to raise thetemperature of the fuel cell stack 22. Further, the combustion gas flowsthrough the combustion gas pipe 74 b into the exhaust gas supply port 64a of the heat exchanger 48.

Thus, the combustion gas is supplied into the heating space in the heatexchanger 48, and heats the oxygen-containing gas flowing through theoxygen-containing gas pipes. Then, the combustion gas flows from theexhaust gas discharge port 64 b through the combustion gas pipe 74 cinto the external heat equipment 76.

As described above, since the heated air, the heated fuel gas, and thecombustion gas flow through the fuel cell stack 22, the temperature ofthe fuel cell stack 22 is increased. In the meanwhile, the partialoxidation reformer 44 is heated by the exhaust gas combustor 46. It isdetermined whether or not the partial oxidation reformer 44 is in apredetermined state where operation of the fuel cell stack 22 can beperformed (step S3).

More specifically, as shown in FIG. 3, a high efficiency operation rangewhere highly efficient reaction occurs is determined as a map based onthe temperature and the air/fuel ratio of the partial oxidation reformer44. In the case where the temperature T1 of the partial oxidationreformer 44 is in the range of 700° C.≦T1≦900° C., and the air/fuelratio is in the range of 0.45≦O₂/C≦0.55, it is determined that thereforming state of the partial oxidation reformer 44 is OK.

If it is determined that the reforming state of the partial oxidationreformer 44 is OK (YES in step S3), the process proceeds to step S4. Instep S4, it is determined whether or not the temperature of the fuelcell stack 22 (stack temperature) is T2 (e.g., 650° C.) or more. If itis determined that the stack temperature is T2 or more (YES in step S4),the process proceeds to step S5.

In step S5, it is determined whether or not the fuel cell stack 22 isready for power generation. More specifically, OCV (open-circuitvoltage) of the fuel cell 20 is measured, and if the OCV reaches apredetermined value, then it is determined that the fuel cell stack 22is ready for power generation (YES in step S5). Thus, power generationis started in the fuel cell stack 22 (step S6).

During power generation of the fuel cell stack 22, in the same manner asin the case of the start-up operation, the air flows through theoxygen-containing gas flow field 36, and the fuel gas flows through thefuel gas flow field 38. Therefore, the air is supplied to the cathode 26of each fuel cell 20, and the fuel gas is supplied to the anode 28 ofeach fuel cell 20 to induce chemical reactions at the cathode 26 and theanode 28 for generating electricity.

The air consumed in the reaction (containing unconsumed air) isdischarged as an oxygen-containing exhaust gas to the oxygen-containingexhaust gas channel 68. Further, the fuel gas consumed in the reaction(containing unconsumed fuel gas) is discharged as the fuel exhaust gasto the fuel exhaust gas channel 70. The oxygen-containing exhaust gasand the fuel exhaust gas are supplied to the exhaust gas combustor 46,and consumed in combustion in the exhaust gas combustor 46. When thetemperature of the fuel gas exceeds the self-ignition temperature of thefuel gas, combustion of the air and the fuel gas is started in thecombustion chamber 54.

In step S3, if it is determined that the reforming state of the partialoxidation reformer 44 is NG (NO in step S3), the process proceeds tostep S7. In step S7, the temperature of the partial oxidation reformer44 is adjusted, and the raw fuel and the air (O₂/C) supplied to thepartial oxidation reformer 44 is adjusted.

Further, in step S4, if it is determined that the stack temperature isless than T2 (NO in step S4), the process proceeds to step S8. In stepS8, it is determined whether the temperature of the exhaust gascombustor 46 is a predetermine temperature T3 (e.g., 900° C.) or more.If it is determined that the temperature of the exhaust gas combustor 46is the predetermined temperature T3 or more (YES in step S8), theprocess returns to step S4. If it is determined that the temperature ofthe exhaust gas combustor 46 is less than the predetermined temperatureT3 (NO in step S8), the process returns to step S2.

In the embodiment of the present invention, the heat exchanger 48 isprovided on one side of the fuel cell stack 22, and the partialoxidation reformer 44 and the exhaust gas combustor 46 are provided onthe other side of the fuel cell stack 22. Thus, heat radiation from thefuel cell stack 22 is minimized, and variation in the temperaturedistribution in the fuel cell stack 22 is reduced. Accordingly, the heatenergy loss can be suppressed, and thermally self-sustaining operationis facilitated easily. The thermally self-sustaining operation hereinmeans operation where the operating temperature of the fuel cell can bemaintained only using the heat generated by the fuel cell itself,without requiring any heat supplied from the outside.

Further, the partial oxidation reformer 44 is provided so as to surroundthe exhaust gas combustor 46. In the structure, in the state where theself-ignition temperature is maintained, the fuel exhaust gas and theoxygen-containing exhaust gas discharged from the fuel cell stack 22 canbe supplied into the exhaust gas combustor 46. Accordingly, in theexhaust gas combustor 46, stability in combustion is improved suitably,and thermally self-sustaining operation is facilitated easily.

Moreover, as a reformer, only the partial oxidation reformer 44 isprovided without requiring any steam reformer. Thus, since the watersupply system for supplying water vapor can be omitted, reduction in thenumber of parts can be achieved, and reduction in the cost and size ofthe entire fuel cell module 12 is achieved.

Further, the heat exchanger 48 is provided at one side of the fuel cellstack 22 in the stacking direction indicated by the arrow A, and thepartial oxidation reformer 44 and the exhaust gas combustor 46 areprovided on the other side of the fuel cell stack 22 in the stackingdirection. Thus, variation of the temperature distribution in thestacking direction of the fuel cell stack 22 can be reduced, loss of theheat energy can be suppressed, and thermally self-sustaining operationcan be facilitated easily.

The heat exchanger 48 is provided above the fuel cell stack 22 in thedirection of gravity, and the partial oxidation reformer 44 and theexhaust gas combustor 46 are provided below the fuel cell stack 22 inthe direction of gravity. Thus, firstly, heat energy produced in thepartial oxidation reformer 44 and the exhaust gas combustor 46 isutilized for raising and maintaining the temperature of the fuel cellstack 22. Thereafter, the heat energy produced in the fuel cell stack 22is used for raising the temperature of the oxygen-containing gas in theheat exchanger 48. Thus, heat release from the entire fuel cell module12 is suppressed as much as possible, loss of the heat energy can besuppressed, and thermally self-sustaining operation can be facilitatedeasily.

Further, the combustion gas pipes 74 a, 74 b, and 74 c are provided forsupplying the combustion gas discharged from the exhaust gas combustor46 to the fuel cell stack 22, the heat exchanger 48, and the externalheat equipment 76 successively. In the structure, firstly, the heatenergy produced in the partial oxidation reformer 44 and the exhaust gascombustor 46 is used for raising and maintaining the temperature of thefuel cell stack 22. Thereafter, the heat energy produced in the fuelcell stack 22 is used for raising the temperature of theoxygen-containing gas in the heat exchanger 48. Further, the heat energycan be supplied to the external heat equipment 76 such as a water heateror a thermoelectric converter by the exhaust gas discharged from theheat exchanger 48. Thus, heat release from the fuel cell module 12 canbe minimized as a whole. Loss of heat energy can be suppressed, andthermally self-sustaining operation can be facilitated easily.

Further, the fuel cell module 12 is a solid oxide fuel cell module.Therefore, the fuel cell module 12 is applicable to high temperaturetype fuel cells such as SOFC.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

The invention claimed is:
 1. A fuel cell module comprising: a fuel cellstack formed by stacking a plurality of fuel cells in a stackingdirection for generating electricity by electrochemical reactions of afuel gas and an oxygen-containing gas; a partial oxidation reformer forreforming a mixed gas of a raw fuel chiefly containing hydrocarbon andan oxygen-containing gas thereby to produce the fuel gas, and supplyingthe fuel gas to the fuel cell stack; an exhaust gas combustor forcombusting the fuel gas discharged from the fuel cell stack as a fuelexhaust gas and the oxygen-containing gas discharged from the fuel cellstack as an oxygen-containing exhaust gas thereby to produce acombustion gas; and a heat exchanger for raising the temperature of theoxygen-containing gas by heat exchange with the combustion gas, andsupplying the oxygen-containing gas to the fuel cell stack, wherein theheat exchanger is provided on one side of the fuel cell stack, and thepartial oxidation reformer, which is alone provided as a reformer in thefuel cell module, and the exhaust gas combustor are provided on theother side of the fuel cell stack; the partial oxidation reformer isprovided so as to surround the exhaust gas combustor, and a combustiongas pipe is provided for supplying the combustion gas discharged fromthe exhaust gas combustor to the fuel cell stack, the heat exchanger,and external heat equipment successively.
 2. The fuel cell moduleaccording to claim 1, wherein the heat exchanger is provided on one sideof the fuel cell stack in the stacking direction; and the partialoxidation reformer and the exhaust gas combustor are provided on theother side of the fuel cell stack in the stacking direction.
 3. The fuelcell module according to claim 2, wherein the heat exchanger is providedabove the fuel cell stack in the direction of gravity; and the partialoxidation reformer and the exhaust gas combustor are provided below thefuel cell stack in the direction of gravity.
 4. The fuel cell moduleaccording to claim 1, wherein the fuel cell module is a solid oxide fuelcell module.